According to the ICM, you need 47.16% equity against the BB's range to call the push. You are getting almost 3:2 odds and you are only a little risk-averse 6-handed against a player you cover by a bit who has close to the starting stack. Here is the output from ICM Explorer:
Fold: 1715 chips, 0.137, SD: $16.07
Win: 3850 chips, 0.2658
Lose: 240 chips, 0.0221
Tie: 2045 chips, 0.1592
Equity needed: 47.16%
Chip odds: 40.86%
Risk premium: 6.3%
Do you have 47% equity with 77? Against a maniac, or some good aggressive restealers, 77 has enough equity since the BB would resteal with a range like 22+ A2s+ A7o+ KQo and some suited broadways. Against one such range, 77 has 53% equity making this a clear call. However, an unknown player in a low stakes tournament probably defends much more often by calling rather than by restealing. If you give the big blind a tighter range of 55+ AT+ KQs, then 77 only has 45% equity and you should fold. (88 would be a close call against that range.) You will see some strange resteals with weak hands, while other players will flat-call with strong hands, but I think the restealing range is tighter than the second range and that you can fold 77.
In theory, when someone resteals for 15 bb against a button raise, you would like to be able to call with a lot of your opening range. If you don't call resteals very often, then you will be exploitable by aggressive restealing, and 77 is pretty good compared with a lot of the stuff you might open on the button. However, this does not mean your opponents are good enough to recognize this and to exploit a tendency to raise/fold too often, and so you can fold hands as good as 77. If you move up into more aggressive games, you might routinely call 15 bb resteals with 77.